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Display panels today open the door to the repository of knowledge, and their use is expanding from conventional home appliances to transparent, wearable and mobile devices. Organic semiconductors are a perfect candidate for this ubiquitous use of display panels since organics are flexible, transparent with high brightness and capable of good color rendering. The expanding outdoor use of organic devices poses questions whether: i) the devices are bright enough to be visible under daylight, and ii) the devices can withstand extreme conditions such as the interior of an automobile in the summer. Organic light emitting devices (OLEDs) achieved ~100% internal quantum efficiency with phosphorescence in 1998 [1], and since then the bottle neck for OLED brightness has been the outcoupling efficiency. The capability of organics to withstand severe conditions is closely related to their morphological stability. Thus, improving the outcoupling efficiency and controlling the morphology of OLEDs are the two crucial aspects in the future display technology. In this sense, this thesis mainly deals with the methods to improve the light outcoupling of OLEDs by morphological control. Also, methods for understanding organic film morphology are discussed. In this thesis, we demonstrate a measurement technology to obtain precise nanoscale information about the morphologies of several organic thin film structures using Fourier plane imaging microscopy (FIM). We use FIM to detect the orientation of molecular transition dipole moments from an extremely low density (i.e. small fractions of a monolayer) of luminescent dye molecules, which we call “morphology sensors.” The orientation of the sensor molecules is driven by the local film structure, and thus can be used to determine details of the host morphology without influencing it. We use symmetric planar phosphorescent dye molecules as the sensors that are deposited into the bulk of organic film hosts during the growth. Furthermore, we monitor morphological changes arising from thermal annealing of metastable organic films that are commonly employed in photonic devices. Methods to control the organic film morphology to improve the light outcoupling are also demonstrated. Here we control the orientation of Pt complex molecules during the growth of emissive layers by two different methods: modifying the molecular structure, and using structural templating. Pt complex dopant molecules whose structures are modified by adjusting the ligands show an approximately 20% increased fraction of horizontally aligned transition dipole moments compared to the original molecule while being diluted in the host matrix. Alternatively, we pre-deposit a highly ordered structural template layer, which results in a 60% increase in horizontally aligned transition dipole moments compared to the film deposited in the absence of the template. Finally, we employ a 2-dimensional transition metal dichalcogenides as the active luminescent layer due to its optimum emission profile for efficient outcoupling. Therefore, a hybrid light emitting device (LED) is fabricated employing a chemical-vapor-deposition grown, centimeter-scale monolayer of WS2 (mWS2), embedded within conductive organic layers. As a result, LEDs with an average external quantum efficiency of 0.3 ± 0.3% and with the highest efficiency of 1% were achieved. Also, we show that negatively charged excitons, also known as trions, are generated in the mWS2 with the injected current, causing an efficiency roll-off at high current densities.

Since their discovery, organic electronic materials have been of great interest as an alternative active layer material for active area materials in electronic applications. Initially studied as probes or lasing material the field has progressed to the point where both conjugated polymers and small organics have become fashionable objects of current device oriented solid state research. Organic electronic materials are liquid crystalline materials, packing into well-ordered domains when annealed thermally or via solvent annealing. The macromolecular orientation of the molecules in the solid state causes a shift in the electronic properties due to coupling of the dipoles. The amount of interaction between molecules can be correlated to different nanoscale morphologies. Such morphologies can be measured using microscopy techniques and compared to the spectroscopic results. This can then be extrapolated out to infer how the charges move within a film. Cyanine dyes represent an interesting form class of dyes as the molecular packing is strongly affected by hydrophilic and hydrophobic pendent groups, which cause the dye to arrange into a tubular bilayer. Spectroelectrochemistry is used to monitor and controllably oxidize the samples. Using singular value decomposition (SVD) it is possible to extract each electronic species formed during electrochemical oxidation and model the proposed species using semi empirical quantum mechanical calculations. Polyfluorene is a blue luminescent polymer of interest for its high quantum yield. The solution and solid-state conformation has shown two distinct phases. The formation of the secondary phase shows a dependence on the molecular weight. In a poor solvent, as the molecular weight increases, the secondary phase forms easier. In the solid state, the highly efficient blue emission from polyfluorene is degraded by ketone defects. The energy transfer to preexisting ketone defects is increased as the filmed is thermally ordered. Glass transitions of block copolymers are studied using synthetically novel polymers where an environmentally sensitive fluorescent reporter is placed within various regions of a self-assembled film. Different dynamics are observed within the block of the film then specifically at the interface of two blocks.